Marked suppression of the activity of some, but not all, antifolate compounds by augmentation of folate cofactor pools within tumor cells

Rongbao Zhao, Feng Gao, I. David Goldman

Research output: Contribution to journalArticlepeer-review

63 Scopus citations


Folates have been co-administered with some antifolates to diminish host toxicity; however, the extent to which this will reduce antitumor activity is not known. To further clarify this issue, studies were undertaken to characterize and quantitate the impact of alterations in intracellular folate levels on the activities of a variety of antifolates in L1210 murine leukemia cells. Intracellular folate cofactor levels increased almost in proportion to the increase in extracellular 5-formyltetrahydrofolate (5-CHO-THF) over a concentration range that encompassed physiological levels of 5-methyltetrahydrofolate. This resulted in a spectrum of increases in the ic50 values of antifolates upon continuous exposure to drugs [Lometrexol (DDATHF) (70x) > trimetrexate (TMQ) (30x), multitargeted antifolate, LY231514 (ALIMTA) (30x) > Raltitrexed, Tomudex (ZD1694) (10x), 6R-2′,5′-thienyl-5,10-dideazatetrahydrofolic acid (LY309887) (10x) > methotrexate (MTX) (6x) > (2S)-2-{o-fluoro-p-[N-(2,7-dimethyl-4-oxo-3,4-dihydroquinazolin-6- ylmethyl)-N-(prop-2-ynyl)amino]benzamido}-4-(tetrazol-5-yl) butyric acid (ZD9331) (3x), Nα-(4-amino-4-deoxypteroyl)-Nδ- hemiphthaloyl-l-ornithine (PT523) (3x)]. Upon a 4-hr pulse exposure to drug, the ic50 values for DDATHF and ALIMTA were increased > 180- and 5-fold, respectively, with only a 2.5-fold increase in the extracellular 5-CHO-THF level within the physiological range. The reductions in drug sensitivities could be attributed to decreases in accumulation of polyglutamate derivatives of ALIMTA and DDATHF. Hence, in these studies, natural folates diminished the activity of agents that undergo polyglutamation by suppression of the formation of these active congeners at the level of folylpolyglutamate synthetase. For inhibitors of dihydrofolate reductase, the suppressive effect of endogenous folates appears to be due to competition between the antifolate and dihydrofolate at the level of the target enzyme. These data should be carefully considered in the design of regimens with antifolates, which incorporate co-administration of folates.

Original languageEnglish (US)
Pages (from-to)857-865
Number of pages9
JournalBiochemical Pharmacology
Issue number7
StatePublished - Apr 1 2001


  • Antifolate
  • Drug resistance
  • Folate cofactors
  • Polyglutamation

ASJC Scopus subject areas

  • Biochemistry
  • Pharmacology


Dive into the research topics of 'Marked suppression of the activity of some, but not all, antifolate compounds by augmentation of folate cofactor pools within tumor cells'. Together they form a unique fingerprint.

Cite this